12 August 2007
I am researching arc building.
I came across a pamphlet called Exploring the Night Sky With Binoculars that I bought years ago which has a good chapter on the size of things.
A Brief Cosmic Glossary Lesson
You will see some impressive sights when you start exploring the night sky with binoculars. Some of the immediate questions that arise are phrased in the form, “How many . . . ?” “How big . . . ?” “How far . . . ?” “How old . . . ?” The difficulty comes in knowing how to understand the answers once they are given. How do you visualize a million or a billion of anything? To comprehend numbers such as these you need a set of mental pictures. If your experience with numbers is so negative that you are getting an anxiety attack already, you might want to skip to the next section. If you would like to come to grips with the numbers of astronomy, the following mental pictures may help.Big Numbers
Most people can visualize a hundred of something. You can count to 100, and you think in terms of dollars and cents all the time. To visualize a thousand of something, compare a grain of sand to a yard stick. A thousand courses of sand grains lined up would measure about a yard. This picture depends, of course, on how big each grain of sand is, but approximate numbers are god enough for our purposes. The main idea is to get in the right ballpark.A million is a thousand thousands, so picture a thousand rows of a thousand grains of sand. Side by side these rows would cover an area one square yard. Swept up, this much sand would just about fill a quart container. Stretched out into a line it would extend a little over half a mile [~5 NYC N/S blocks].
A billion grains of sand would be a thousand layers of a million grains each, and would occupy a cubic yard. A trillion grains of sand (1000 cubic yards) would fill a container 10 yards on each side. We won’t talk about any numbers larger than this.
Sizes and Distances
Now let’s apply our number images to the cosmos. Our galaxy has somewhere between 100 billion and a trillion stars. Think of something that has a volume of 100 to 1000 cubic yards, a large swimming pool perhaps, and imagine it filled with sand. That’s a lot of sand! It is an interesting coincidence that the observable universe has about as many galaxies as a single galaxy has stars, so we can use the same picture here.Let’s work our way up through the cosmic distance scale. The earth is about 8000 miles across. The moon is about a fourth as big and about 30 earth diameters (about a quarter million miles) away. Jupiter, the largest planet, is about ten times the size of the earth, and the sun is about ten times the size of Jupiter. That makes the sun a little under a million miles across. The earth is nearly 100 million miles from the sun, so if we pictured the sun to be the size of our standard grain of sand, the earth would be about 3 ½ inches away. The earth would be too small to see and the entire orbit of the moon would be half the size of the sand grain representing the sun. Jupiter would b e 1 ½ feet from the sun, and Pluto would be about 12 feet away. Thus the whole solar system, as we have pictured it, would easily fit on half a tennis court. The solar system is mostly just a star, the sun. The planets, their moons, and a few smaller chunks of rock and ice, called asteroids and comets, respectively, are some of the debris left over from the sun’s formation. One of those little specks is pretty important to those of us who call it home, but in terms of comparative size, it is a speck nonetheless.
The next star, on this scale, would be another sand grain 15 miles away. This is typical of the spacing between stars in our part of the galaxy. The galaxy as a while, as we said earlier, contains between a hundred billion and a trillion stars. Now picture spreading out all that sand into a disk with 15 miles between grains. The model itself would extend out beyond the moon! To keep going beyond this point we need to change the scale of our model. Picture our galaxy reduced now to b e the size of a nickel. On this revised scale the Andromeda galaxy, our nearest large neighbor, would be the size of a quarter about 18 inches away. The entire observable universe would extend outward nearly three miles in all directions. What lies beyond that is hard to say.
Time
Space and time are inextricably woven together. As we look out in space the light we see took time to get here, so we are seeing light that originated in the past. Thus as we look out in space we are also looking back in time. Light, traveling at 186,000 miles per second, takes over a second to come from the moon, 8 minutes to come from the sun, 5 hours to come from Pluto, 4 ½ years to come from the next star, 100,000 years to cross the galaxy, and 2 million years to come from the Andromeda Galaxy. The universe is estimated to be about 20 billion years old, so however large the universe may be, we cannot observe out to distances greater than 20 billion light years.Picture a time scale where the size of a grain of sand represents a million years. Then a yard represents a million years and 20 yards represents the estimated age of the universe. The sun and its planets formed about 4.6 million years ago, not at the beginning of time as many people assume. The sun has an estimated stable life span of 10 or 12 billion years, so we are nearly half way through the sun’s life cycle. The sun revolves around the galaxy ion a couple hundred million years, so we have been around about twenty times since the sun and the planets formed. The most massive stars are like cosmic flash bulbs. They burn their fuel at a tremendous rate and have life spans of only about a million years, which carries them only a few degrees around the galaxy before they burn out.
“How do we know all of this?” you ask. If you are interested in digging into the meat of astronomy there are many well written, non-mathematical astronomy texts available today. A good place to inquire is at a local community college bookstore.
Now, lets get back to observing.
All of that got me working in Excel to try to graphically display the universe. For my source of base statistics I used the Audubon astronomy field guide.
I got drowned this morning and it is still cloudy tonight and should be through the weekend. But I did some astronomy anyway with Peter and Kin, sort of.
Every year on this date there are celebrations of Yuri’s Night worldwide. I have never been aware of them before and there has never been one before in NYC. Tonight we attended one staged by the CUNY Graduate Center.
The event was half art and half short lectures. It started out with a presentation of some software that some media students wrote that loosely mimicked the solar system and assigned sounds to each object. The sounds were varied by the location of the object and its size on the screen. As the moon of a planet passed through the field of view the volume of its sound grew then faded. It was interesting but not worth the amount of time allotted to it. Then they brought them back to do it again as a four player game.
Ed Balbruno, who has some kind of association with John Pazmino and AAA, gave a talk on his live and times at NASA where he was fired because he wouldn’t stop working on a project that NASA considered unproductive at the time. He had an idea that you could get to the Moon a lot cheaper by letting the satellite swing out on a long eccentric orbit that would intersect with the gravity field of the Moon where it would be captured and would be more fuel efficient than the Hohmann Transfer Orbit which requires the expenditure of rocket fuel to brake the spacecraft and drop it into orbit. His orbit has been used by the Japanese. But it takes two years to readh the Moon so is not practical for manned missions.
Next up was Tom Henricks who was an STS pilot and commander on four missions and has left NASA and is not President of Aviation Week magazine. He gave an interesting short talk on his experience flying the STS in the pre ISS era. He had a video from the flight deck on launch that showed the violence of the launch and said that 1 in 20 astronauts who have ever flown on the Shuttle have died on it.
The last talk was by Greg Olsen who is one of the Americans who has made a tourist flight to the ISS. He was interesting and talked practically about the experience. After the event I asked him about the experience of landing on land and he said that it wasn’t bad. The seats are padded and mounted on springs. The pictures they showed of Yuri’s capsule (I think that is what it was) after landing didn’t appear to have even dented the soil.
Last on the lineup was Carter Emmart from the Hayden Planetarium who did a digital universe tour accompanied by a violin player who played new age music. This was another nice show but it lasted too long. At the beginning I recognized the Hyades and the Pleiades and at the end I saw Orion. Peter said the star field was upside down.
It was an OK event for free but I would have liked more lectures from the astronauts and less art.
posted by Charlie at 13:33
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